Learn By Doing – Logic of Hypothesis Testing

For many years “working full-time” has meant 40 hours per week. Now it seems that corporate employers expect their employees to work more than this amount. A researcher decides to investigate this hypothesis.

Claim 1: The average time full-time corporate employees work per week is 40 hours.

Claim 2: The average time full-time corporate employees work per week is more than 40 hours.

To substantiate his claim, the researcher randomly selects 250 corporate employees and finds that they work an average of 47 hours per week with a standard deviation of 3.2 hours.

According to the Center for Disease Control (CDC), roughly 21.5% of all high-school seniors in the United States have used marijuana. (Comments: The data were collected in 2002. The figure represents those who smoked during the month prior to the survey, so the actual figure might be higher). A sociologist suspects that the rate among African-American high school seniors is lower, and wants to check that. In this case, then,

Claim 1: The rate of African-American high-school seniors who have used marijuana is 21.5% (same as the overall rate of seniors).

Claim 2: The rate of African-American high-school seniors who have used marijuana is lower than 21.5%.

To check his claim, the sociologist chooses a random sample of 375 African-American high school seniors, and finds that 16.5% of them have used marijuana.

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This material was adapted from the Carnegie Mellon University open learning statistics course available at http://oli.cmu.edu and is licensed under a Creative Commons License. Other materials used in this project are referenced when they appear.

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